#include <iostream>

using namespace std;

const int N = 1e4 + 10;
int a[N],b[N];

int n;

int check1()
{
    a[1] = 0;
    for(int i = 2;i <= n+1;i++)
    {
        a[i] = b[i-1] - a[i-1]-a[i-2];
        if(a[i]<0||a[i]>1)
        {
            return 0;
        }
    }
    if(a[n+1] == 0)
    {
        return 1;
    }
    return 0;
}

int check2()
{
    a[1] = 1;
    for(int i = 2;i <= n+1;i++)
    {
        a[i] = b[i-1] - a[i-1]-a[i-2];
        if(a[i]<0||a[i]>1)
        {
            return 0;
        }
    }
    if(a[n+1] == 0)
    {
        return 1;
    }
    return 0;
}

int main()
{
    cin >> n;
    for(int i = 1;i <= n;i++)
    {
        cin >> b[i];
    }
    int ret = 0;
    ret += check1();
    ret += check2();
    cout << ret << endl;
    return 0;
}